Dilated cardiomyopathy and heart failure are a leading cause of mortality in developed countries. However, the proteins contributing to cardiac dysfunction are poorly defined. The long-term objective of this proposal is to define the role(s) that alphaB-crystallin (CryAB) plays in human heart failure. CryAB is a small heat shock protein, which functions as a molecular chaperone. An Arg120Gly missense mutation in CryAB (CryABR120G) causes desmin related myopathy. Cardiac-specific overexpression of CryABR120G produces a dilated cardiomyopathy and heart failure, confirming the human cardiac pathology. CryABR120G hearts display both mitochondrial dysfunction, and apoptotic induction while progressing to heart failure. The goal of this proposal is to test if the CryABRI 20G pathology is due to m itochondrial dysfunction and/or apoptosis. Specific Aim 1 will test the hypothesis that VDAC1 is necessary for CryABRI 20G induced mitochondrial dysfunction. VDAC1, a mitochondrial pore component, interacts directly with the mutant protein. The hypothesis is that the CryABR120G-VDAC1 interaction is causative in the development of mitochondrial dysfunction. The hypothesis will be tested by crossing CryABRI20G mice with vdad-null mice, which will determine whether VDAC1 ablation is sufficient to rescue m itochondrial dysfunction. Molecular, histological and physiological analyses will be employed to comprehensively interrogate the effects of these crosses. Specific Aim 2 will determine if the onset of apoptosis is necessary for the irreversible development of heart failure in the CryABRI20G model. Preliminary data show increasing early, mid, and late markers of apoptosis as CryABRI 20G hearts progress towards failure. To test this aim, mice with inducible, cardiac-specific expression of CryABR120G will be used to define the stage at which heart failure becomes irreversible and correlate that with apoptotic indices and other biological markers. Identifying the decisive pathogenic step(s) after which the development of heart failure becomes irreversible may help define therapeutic windows for successful treatment of heart disease. The goal of this proposal is to test the roles of mitochondrial dysfunction and apoptosis in developing heart failure. First, the necessity of a protein (VDAC1) in mitochondrial dysfunction will be tested. Second the point at which cardiac cell death can be reversed will be identified. Understanding the timing and necessity of these two facets of heart failure may help define the therapeutic timing and targets for treatment of heart disease.